Display devices such as a liquid crystal display device, an organic EL (electroluminescence) display device, a flexible display device, and an electronic book are typically provided with an active matrix substrate (also referred to as a “TFT substrate”) in which thin film transistors (also referred to as “TFTs” below) are formed as switching elements for respective pixels.
The active matrix substrate includes a plurality of data lines, a plurality of gate lines, a plurality of TFTs disposed for respective intersections thereof, pixel electrodes that apply a voltage to an optical modulation layer such as a liquid crystal layer, auxiliary capacitance wiring lines, auxiliary capacitance electrodes, and the like.
An example of a liquid crystal display device using an active matrix substrate is disclosed in Patent Document 1. FIG. 20 is a plan view showing a part of a plurality of pixels in the active matrix substrate disclosed in Patent Document 1. As shown in FIG. 20, this active matrix substrate includes pixel electrodes 130 and TFTs 140 respectively provided for a plurality of pixels, a plurality of gate lines (scan lines) GL, and a plurality of data lines (signal lines) DL that extend in a direction perpendicular to the plurality of gate lines GL.
In the liquid crystal display device of Patent Document 1, MFD (multi-field driving) is employed in order to increase a writing time to the pixel electrodes 130 and to mitigate flickering. In order to realize the MFD, in this active matrix substrate, two data lines DL extend between two pixel electrodes 130 adjacent to each other in the horizontal direction. Also, in order to increase the aperture ratio, each gate line GL is provided for two pixel electrodes 130. In other words, two pixel electrodes 130 are disposed between two gate lines GL that are adjacent to each other in the vertical direction.
The active matrix substrate is used not only for a display device, but also as a substrate for an image sensor. In the image sensor, photodiodes are disposed on the active matrix substrate for the respective pixels. When light enters the photodiodes, electrical charges are generated due to the photoelectric effect, and the generated electrical charges are temporarily stored in the plurality of pixel electrodes (or pixel capacitances). The stored electrical charges are sequentially read out to the signal lines by turning on and off the respective TFTs through the control signal from the scan lines. This way, an image that entered the image sensor is converted to an image signal. It is also possible to provide a conversion layer that directly converts incident light to electrical charges, instead of photodiodes.
Patent Document 2 discloses a liquid crystal display device and an image sensor that have an active matrix substrate. FIG. 21 is a plan view showing a part of the active matrix substrate disclosed in Patent Document 2. As shown in FIG. 21, the active matrix substrate includes TFTs 140 respectively provided for a plurality of pixels, lower pixel electrodes 130a, upper pixel electrodes 130b, pixel capacitance electrodes (auxiliary capacitance electrodes) 410, a plurality of gate lines GL, a plurality of data lines DL, and a plurality of pixel capacitance lines (auxiliary capacitance lines) SL.
In each pixel, the lower pixel electrode 130a and the upper pixel electrode 130b are connected through a contact hole 720 formed in an insulating layer between the two electrodes, and the lower pixel electrode 130a and the upper pixel electrode 130b function as a pixel electrode. The pixel capacitance line SL and the pixel capacitance electrode 410 are connected through a contact hole 400. A pixel capacitance (auxiliary capacitance) 140a is formed by the pixel electrode, the pixel capacitance electrode 410, and a dielectric layer between the two electrodes.
Patent Documents 3 and 4 disclose a display device, an electronic paper, an electronic writing device, and the like that utilize the electrophoresis method. FIGS. 4 and 5 in Patent Document 3, and FIGS. 1 and 2 in Patent Document 4 illustrate configurations of an active matrix substrate for such display devices and the like.